a) Preheat your oven to 240°C/220°C fan/gas mark 9. 

b) Chop the sweet potato into 2cm chunks (no need to peel).

c) Put the sweet potato chunks onto a large baking tray. Drizzle with oil, season with salt and pepper, then toss to coat. Spread out in a single layer. TIP: Use two baking trays if necessary.

d) When the oven is hot, roast on the top shelf until golden, 18-20 mins. Turn halfway through.

a) Meanwhile, trim the root and dark green leafy part from the leek and discard.

b) Halve lengthways, then thinly slice.

c) Heat a drizzle of oil in a large saucepan on medium-high heat.

d) Once hot, add the leek and season with salt and pepper. Cook the leek, stirring occasionally, until softened, 4-6 mins.

a) While the leek fries, peel and grate the garlic (or use a garlic press).

b) Drain and rinse the butter beans in a sieve. 

c) Once the leek has softened, add the garlic to the pan and fry until fragrant, 1 min.

a) Stir in the creme fraiche, vegetable stock paste, sun-dried tomato paste, butter beans, sugar and water for the soup (see pantry for both amounts).

b) Bring to the boil, then reduce the heat and simmer until thickened, 4-5 mins.

a) Meanwhile, halve the burger buns. Toast the burger bun halves in your toaster until golden.

b) When the soup has thickened, stir in the cheese and spinach a handful at a time, until the cheese has melted and the spinach is wilted and piping hot, 1-2 mins.

c) When the sweet potato is roasted, stir it into the soup.

d) Taste and season the soup with salt and pepper. Add a splash of water if it's a little too thick.

a) Share the soup between your serving bowls.

b) Cut the burger bun halves in half and serve alongside for dipping.